This invention relates generally to vapor compression refrigeration systems and, more particularly, to a method and apparatus for subcooling refrigerant in a transport refrigeration system.
In many refrigeration systems, such as those for preserving food in supermarkets, refrigerators and the like, the load is substantially fixed and the demands of the system are substantially constant throughout the life of the system.
Transport refrigeration systems are different. As the types of food products that are being transported in refrigerated trucks, trailers and containers are always changing, the temperatures at which these products are desirably maintained also change. For example, one day the cargo of a truck may be bananas, with the desired temperature to be maintained at 57xc2x0 degrees. On the next day, the same trailer may be hauling frozen goods, and the desired temperature to be maintained in the trailer would be 0xc2x0 F. or below. They also must be able to operate in all ambient conditions as they are portable and need to be able to operate all over the world. Because of this wide range of demands, the design of a refrigeration system for a transport truck/trailer must therefore be very flexible. Thus, they must be designed to meet the maximum capacity requirements, but they are preferably designed to operate efficiently and precisely at much lower capacity requirements during most of their operating life.
Various marketing conditions have tended to exacerbate the problems of meeting the capacity requirements of transport refrigeration systems as discussed hereinabove. For example, because of environmental concerns, it has become necessary to abandon the use of more efficient, but environmentally undesirable, refrigerants, and to replace them with refrigerants that are less efficient. Another development that has occurred because of the need for greater cargo capacity and overall efficiencies, is a tendency to lengthen the refrigerated trailers, and also construct them with thinner side walls.
Current single stage compression systems have limited capacity and cannot meet the market needs as discussed hereinabove. The use of subcooling and refrigeration systems has long been used but the systems have generally been relatively complex, expensive, and difficult to maintain. Examples of such systems include those with suction liquid heat exchangers, subcoolers in condenser coils, and mechanical subcoolers using separate compressors or economizer subcoolers in multi-compressor staged systems.
It is therefore an object of the present invention to provide an improved transport refrigeration system.
Another object of the present invention is the provision in a transport refrigeration system to selectively operate at higher capacity levels in an easy to use and efficient manner.
Yet another object of the present invention is the provision in a transport refrigeration system for operating at a lower capacity level in a reliable and efficient manner.
Still another object of the present invention is the provision for transport refrigeration systems which can be readily and easily boosted in its output capacity.
Yet another object of the present invention is the provision for a transport refrigeration system which is economical to manufacture and effective and efficient in use.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.
Briefly, and in accordance with an aspect of the invention, a single compressor of a transport refrigeration system is provided with two sections, with one section being connected to the main system evaporator, and the other section being connected to a subcooling evaporator. An isolation valve and an expansion device are in the subcooler unit so as to allow for control and isolation of the subcooler when not required.
In accordance with another aspect of the invention, a multiple cylinder reciprocal compressor is provided with one or more cylinders being dedicated to use in the subcooler circuit, while the other cylinders are dedicated to the main evaporator circuit.
By yet another aspect of the invention, one or more unloading circuits are provided in the main section of the compression system such that the compressor can be unloaded during periods of low capacity demand.
In the drawings as hereinafter described, a preferred embodiment is depicted; however, various other modifications and alternate constructions can be made thereto without departing from the true spirit and scope of the invention.